Terminal bushing having recessed spring assembly with electrostatic shielding construction



J y 13, 1967 c. F. SONNENBERG ETAL 3,331,918

TERMINAL HING HAVING RECESSED SPRING ASSEMBLY WITH E CTROSTATIC SHIELDING CONSTRUCTION 4 Sheets-Sheet Filed Oct. 13, I965 y 18- 6 c. F. SONNENBERG ETAL 3,

7 TERMINAL BUSHING HAVING RECESSED SPRING ASSEMBLY WITH ELECTROSTATIC SHIELDING CONSTRUCTION Filed Oct; 13, 1965 4 Sheets-Sheet 5 FIG. 6.

July 18, 9 c F SONNENBERG E L 3,331,918

NG RECESS TERMINAL BUSHING HAVI ED SPR N ASS LY WITH ELECTROSTATIC S HIELDING CONSTRUCTI Filed Oct. 13, 1965 4 Sheets-Sheet 4 FIG. 9.

if 0 1 ii 25% 4' \v Q 10% Q g PRIOR ART and thereby to eliminate one of the United States Patent TERMINAL BUSHING HAVING RECESSED SPRING ASSEMBLY WITH ELECTROSTATIC SHIELDING CONSTRUCTION Charles F. Sonnenberg, Penn Hill Township, Pittsburgh,

and James H. Frakes, Pittsburgh, Pa, assignors to Westiughouse Electric Corporation, Pittsburgh, Pa, a corporation of Pennsylvania Filed Oct. 13, 1965, Ser. No. 495,613 8 Claims. (Cl. 174-142) This invention relates generally to terminal bushings having spring assemblies for maintaining compressive force upon the insulating casing elements, and, more particularly, to an improved terminal-bushing construction having a recessed spring assembly, which, in addition, serves as an electrostatic shield for the spring elements.

A general object of the present invention is to provide an improved terminal bushing having a recessed spring assembly in which the axial length of the terminalbushing assembly may be maintained at a minimum, thereby providing a minimum spacing between the modular interrupting units of a multi-break type of circuit interrupter.

Another object of the instant invention is to provide an improved terminal-bushing construction which will be accurately assembled in a minimum length of time.

Still a further object of the present invention is to provide an improved spring assembly which may be prestressed prior to assembly, and in which the component parts thereof may be accurately placed into their proper position.

Another object of the present invention is to provide an improved recessed-type of spring assembly for a terminal bushing having a minimum number of component parts.

Another object of the present invention is to provide an improved terminal assembly for a terminal bushing involving a spring assembly in which novel gasketing means are provided to take the place of soft solder joints, most troublesome causes of insulation gas leakage.

Still a further object of the present invention is to provide an improved terminal-bushing construction for a compressed-gas type of circuit interrupter, in which gas from the interrupting module is permitted to leak into the interior of the terminal bushing, and to provide improved sealing means for preventing the leakage or escape of such gas from the interior of the terminal bushing.

Another object of the present invention is to provide an improved terminal-bushing construction which may be rapidly assembled and disassembled in a convenient manner.

An ancillary object of the present invention is to provide an improved recessed-type of spring assembly for a terminal bushing in which the electrostatic shielding, adjacent the terminal end of the terminal bushing, is provided by a component element of such spring assembly.

Still a further object of the present invention is to provide an improved spring assembly, such as set forth in the immediately preceding paragraph, in which an adequate clearance is provided between the electrostatic spring bowl and the inner end surface of the insulating casing element for the terminal bushing.

Still a further object of the present invention is to provide an improved method for effecting the assembly of a terminal bushing involving the imposition of axial tension upon the conductor stud and a simultaneous imposi- 3,331,918 Patented July 18, 1967 tion of compressive stress upon the surrounding insulating casing element.

In accordance with one embodiment of the instant invention, a conducting terminal cap has a recessed end portion and is threaded onto the extremity of a conductor stud extending axially through a terminal bushing. The terminal cap has secured thereto a flexible bowl-shaped diaphragm element having an outer flange portion, which is in contiguous relationship with gasketing means provided at the end extremity of the outer insulating casing element. In addition, the construction is such as to permit the insertion of a pre-stressed spring assembly into the aforesaid flexible electrostatic bowl-shaped element, and to permit a subsequent threading of a hollow retaining nut onto the extremity of the terminal cap to thereby permit the loosening and removal of the pre-stressing spring bolts. As a subsequent operation, and forming a component part of the recessed spring bowl assembly, an annular weather shield is secured to the outer face of the interior bowl-shaped spring retainer of the terminal-bushing spring assembly.

Further objects and advantages will readily become apparent upon reading the following specification, taken in conjunction with the drawings, in which:

FIG. 1 is a side elevational view of a multLbreak type of compressed-gas circuit interrupter, involving a number of serially-related interrupting modules, each of which has associated therewith horizontally-extending terminal-bushing structures of a type incorporating the present invention;

FIG. 2 is an enlarged longitudinal sectional view taken through the interior of a terminal-bushing assembly embodying the novel features of the instant invention;

FIG. 3 is an enlarged detailed view taken in crosssection through the spring assembly, which is inserted within the flexible bowl element of the instant invention;

FIG. 4 is a quarter-sectional view taken through the terminal-cap element utilized in the present invention;

FIG. 5 is a quarter-sectional view taken through the hollow retainer nut utilized in the present invention;

FIG. 6 is a fragmentary end elevational view of a spring retainer element or plate used in the improved terminal bushing construction of our invention;

FIG. 7 is a fragmentary end view of the combined terminal-shield ring and recessed spring retainer element of the instant invention; and,

FIGS. 8 and 9 are comparative views showing the improvement in electric field conditions resulting from the use of the present invention.

Referring to the drawings, and more particularly to FIG. 1 thereof, it will be noted that there is shown a high-voltage three-phase compressed-gas circuit interrupter lllincluding three pole-units, only the end poleunit A being illustrated in FIG. 1. As Well known by those skilled in the art, an end view, not shown, of the circuit-interrupting assemblage 10 would reveal three such pole-unit assemblies, each of which would be of the serially-related multi-break type, such as illustrated in FIG. 1. Reference may be had to FIG. 2 of United States patent application filed June 12, 1964, Ser. No. 374,708, now US. Patent 3,291,947, issued Dec. 13, 1966 to Roswell C. Van Sickel entitled Interrupting Structures and Operating Mechanisms for Compressed-Gas Circuit Interrupters, and assigned to the assignee of the instant application.

The pole-units, such as pole-unit A, are alike except for the interpole electrical control wiring, gas lines and air lines, and for the mechanism house on the middle poleunit, Which contains the common parts of the air and gas systems. Each pole-unit, such as the pole-unit A, is

mounted upon a heavy grounded supporting frame 12 comprising heavy longitudinally-extending beam mem'. bers 14 and angularly-braced supports 16. In addition, each supporting frame 12 preferably has a longitudinallyextending high-pressure main reservoir tank 18 associated therewith. Individual high-pressure gas supply pipes, not shown, extend upwardly through three upstanding insulating column structures 22 to supply high-pressure gas to auxiliary high-pressure reservoir chambers, not shown, at high potential, and disposed interiorly within interrupting head units 28. Interiorly of the interrupting heads 28 is also a pair of serially-related arc-extinguishing units not shown, but more particularly illustrated in the aforesaid Patent 3,291,947.

As set forth more in detail in the aforesaid patent, interiorly of each interrupting head-unit 28 is a rotating movable contact assembly carrying arc-extinguishing orifice members therewith, and making separable engagement with stationary contact structures, each of which is secured at the interior end of terminal bushings 34, the construction of which constitutes the essence of the instant invention.

With reference to FIG. 2 of the drawings, it will be observed that extending axially interiorly of each terminalbushing assembly 34 is a hollow conducting tubular terminal stud 36, having one or more gas-entrance holes 37 provided through the sidewall thereof. At the inner end of the hollow conducting terminal stud 36 there is threadedly secured into place a stationary contact foot 40 having a gas-inlet filter cartridge 42, which filters the gas, such as sulfur-hexafluoride (SP gas, which is permitted to flow from the general interior 50 of the interrupting module 28 through suitable provided passages 52, provided in the stationary contact foot 40, and through the interior 60 of the hollow conducting terminal stud 36 to pass outwardly into the region 62, provided within the terminal bushing 34, by way of the inlet apertures 37. As a result, the sulfur-hexafluoride (SP gas pressure provided within the space 62 of the terminal-bushing assembly 34 is at the same pressure as the interior 50 of the interrupting module 28.

A toroidal-shaped mounting flange 70 and mounting bolts 72 are provided to fixedly secure the terminal bushing 34 to the end of the interrupting module 28, the inner insulating casing element 75 of the terminal bushing 34 passing through an opening 77 provided at the end of the interrupting head 28. In addition, there is provided an outer Weatherproof insulating casing 80, the particular surface configuration of the flange elements 83 thereof being set forth in detail and described in United States patent application filed Feb. 7, 1964, Ser. No. 343,369, now US. Patent 3,281,525, issued Oct. 25, 1966 to Chanles F. Sonnenberg and James H, Frakes, entitled High-Voltage Bushing for Horizontal Mounting With Sheds Protecting a Substantial Portion of the Creep Distance Along the Surface of the Bushing From Atmospheric Fall-Out, and assigned to the assignee of the instant application.

It will be noted that the right-hand end of the insulating casing 80, which may be formed of porcelain, is in abutment with the mounting flange 70, a concentric gasketing assembly 82 being provided therebetween, and comprising an inner ring 82a of .QOO-inch thick neoprene, and an outer annular gasket 82b, in the particular construction shown, comprising a %2-ll'1h thick asbestos neoprene stop ring. The inner gasket 8211 provides a gas seal, whereas the outer gasket 82b provides a stop gasket.

An inner terminal flange ring 90 is threadedly secured, as at 91, to the inner extremity of the hollow conductor stud 36 and has an outer flange'portion 90a thereof in abutment with the inner extremity 75a of the inner insulating casing element 75, a gasket 92 being provided therebetween. It will be noted, however, that this gasket 92 need not be gas-tight, inasmuch as a gasket 94 is provitled, which seals the mounting flange 70 from the outer face of the interrupting module 28.

As well known by those skilled in the art, in a terminalbushing construction, it is desirable to apply compressive stress upon the insulating casing elements 75, 80 whereas tensile stress is correspondingly exerted upon the axiallyextending metallic conductor stud 36. Porcelain, of course, is well able to withstand compressive force; and the imposition of compressive force upon the casing elements, such as the elements 70, 75 and 80 of the terminal-bushing, compresses the various gasketing means, and thereby prevents the escape of compressed sulfur-hexafluoride (SP gas from the interior 62 to the region exteriorly of the terminal bushing 34.

To effect this end, namely to apply compressive force upon the sealing gaskets and thereby to prevent the escape of SF gas therethrough, a spring assembly 100 (FIG. 3) is provided, which may be pre-stressed by spring bolts 102 prior to the actual assembly operation upon the terminal bushing 34. In other words, with reference to FIG. 3

. of the drawings, it will be observed that the spring bolts 102 retain the compression springs 104 in compression between an inner bowl-shaped combined terminal-shield ring 106 and an outer spring retainer element or ring 107, which assembly is inserted into position within casing following a previous insertion of a terminal cap 110 (FIG. 4) having a cup-shaped flexible diaphragm electrostatic1 shield element 112 secured thereto, being placed into position, as by being threaded, as at 114, onto the threaded end of the conductor stud 36.

In more detail, the conducting terminal cap 110, having the flexible bowl-shaped diaphragm 112 brazed thereto, as at 116, is threaded onto the left-hand end of the hollow terminal stud 36 as a first operation until the gasketing means is made hand-tight. The gasketing means 120 comprises, as was the case with the gasketing means 82, an inner neoprene ring 120a and an outer stop ring 12% of asbestos neoprene.

Following the threading onto the end of the hollow conducting terminal stud 36 of the assembly comprising the terminal cap 110 and the flexible diaphragm element 112 secured thereto, a neoprene gasket is placed into position in contiguous relationship with an outwardly-extending flange portion 112a of the flexible diaphragm bowl element 112, and the spring assembly 100 is then placed into position, so that an inner portion 106a of the terminal shield ring 106 comes into abutment with the gasketing means 130.

Following the aforesaid operation, the hollow retainer nut 140, more clearly illustrated in FIG. 5 of the drawings, is threaded upon the terminal cap 110 with a gasketmg means 152 provided therebetween. The gasketing means 152 comprises a y g-inch asbestos-neoprene gasket, for example.

When the aforesaid operation is completed, the spring bolts 102 are removed from the tapped openings 106b provided in the bowl-shaped inner spring retainer 106; and this operation will permit the multiple-spring elements 104 to exert compressive stress, by means of the terminalshield ring 106, upon the outer ceramic casing 80, and simultaneously to exert compressive force upon the outer spring-retainer plate 107. It will be noted that there is a clearance between the hollow retainer nut and the inner wall surface of the outer spring plate 107. In addition, it will be noted that there is a permissible sliding action, which may take place between the inner surface of the terminal-shield ring 106 and the outer side surface 110a of the terminal cap 110.-

Following the removal of the spring-mounting bolts 102, which have been utilized to provide a pre-stressing of the spring assembly 100, an annular weather shield plate may be secured into place by means of a plurality of mounting bolts 161. Gasketing means, such as a gasket 162 of annular configuration, and an additional gasket 164, being of the O ring type, may be employed. It will, however, be noted that the gasketing means 162,

J 164 does not have to withstand gas pressure, inasmuch as the gasketing means 120 provides the necessary gas seal.

From the foregoing construction, it will be apparent that a terminal bushing 34 has been provided, being par ticularly useful for use on live-tank high-voltage circuit breakers, having a number of advantageous features. First, the bushing-spring bowl 106 is recessed within the porcelain weather casing 80, without increasing the overall length of the porcelain. This minimizes the terminalbushings length, and, in turn, the spacing between the interrupting columns 22 of a multi-break pole-unit A, such as illustrated in FIG. 1.

In addition, the recessed spring bowl construction serves as an electrostatic shield by reducing the voltage gradient on the surface of, and in the immediate vicinity of the terminal end of the bushing porcelain as shown more clearly in the comparative FIGURES 8 and 9. It will be noted that the equipotential flux lines clearly show a reduction of the voltage gradient adjacent the outer end of the terminal bushing by an application of the invention. This also keeps the porcelain length to a minimum without resorting to an external grading ring complex. The guarantee of at least a small gap between the recessed diaphragm shield 112 and the inside diameter of the porcelain casing 80 as indicated by the spacing S prevents the creation of corona streamers, which would creep along the porcelains interior surface 80a and precipitate internal breakdown.

The absence of solft-solder joints eliminates one of the most troublesome causes of insulation gas leakage. The electrostatic shielding provided by the combination terminal-shield ring and recessed spring shield effectively reduces the RIV level of terminal connectors, or conductors attached to the terminal bushing. The central core of the spring assembly 100, which threads onto the conductor stud 36, is so designed that it can be fabricated from bar-stock rather than be cast. This eliminates leakage because of porous castings. In addition, the disclosed construction permits the use of an aluminum terminal stud 36, which is not exposed to the outside weather since the terminal cap 110 is fabricated out of copper and is the only conducting item exposed to weather.

Although there has been illustrated and described a specific terminal-bushing construction, it is to be clearly understood that the same was merely for the purpose of illustration, and that changes and modifications may readily be made therein by those skilled in the art, without departing from the spirit and scope of the invention.

We claim as our invention:

1. A terminal bushing including an axially-extending conductor stud, a hollow surrounding insulating casing element, a cup-shaped terminal cap member secured to the end of said conductor stud and having a cup-shaped flexible electrostatic shield secured thereto with a gastight seal, said electrostatic shield having a radially-outwardly extending flange portion in abutment with the end of said surrounding casing element, spring means encircling said conductor stud and disposed interiorly of said cup-shaped flexible electrostatic shield for imposing tensile stress upon said conductor stud and corresponding axial compressive force upon said casing element including an annular cup-shaped spring seat support member (106) having a flange portion overlying the outwardlyextending flange portion of said electrostatic shield, said spring assembly also including a complementary spring seat member fixedly supported relevant to said terminal cap member.

2. The combination according to claim 1, wherein a hollow retainer nut is threadedly secured to the end portion of said cup-shaped terminal cap member to retain said complementary spring seat member (107).

3. In combination, a terminal bushing having an axially-extending conductor stud and a surrounding insulating hollow casing element, a terminal cap having a recessed portion threadedly attached to the extremity of said conductor stud and having secured thereto a cup-shaped flexible electrostatic shield having a radially outwardlyextending flange portion, said radially outwardly extending flange portion being in abutment with the end of said hollow casing element, a relatively heavy cap-shaped spring seat member having a radially outwardly extending flange portion in abutment with the radially outwardly extending flange portion of said electrostatic shield member and making sliding engagement with a portion of said terminal cap member, a complementary spring seat member, a plurality of compression springs interposed between said two spring seat members for biasing them apart, and removable supporting means (140) for removably supporting the second-mentioned spring seat member on said terminal cap member.

4. The combination according to claim '3, wherein an annular weather-proof shield is fixedly secured to the radially outwardly extending flange portion of the relatively heavy spring seat member to prevent atmospheric contaminants from entering into the spring area.

5. A terminal bushing including an axially-extending conductor stud assembly and at least one surrounding insulating casing element, a spring assembly at least partially recessed within one end of said insulating casing element and including a cup-shaped spring retainer (106) having a radially outwardly-extending flange portion bearing upon the end face of said insulating casing element, said spring assembly also including a complementary spring retainer (107) acting against one end of said conductor stud assembly, whereby compressive stress is imposed upon the insulating casing element and corresponding tensile stress is exerted upon the conductor stud assembly, a cup-shaped electrostatic shielding element (112) at least partially surrounding said spring assembly and having a radial inner portion sealed to said conductorstud assembly, said cup-shaped electrostatic shielding element also having a radially outwardly-extending flange portion interposed between the flange portion of the cupshaped spring retainer (106) and the end face of the insulating casing element, whereby a fluid seal may be maintained at said one end of the insulating casing element.

6. The combination according to claim 5, wherein the conductor stud assembly includes a hollow conductor stud and a terminal cap secured thereto, and 'wherein the electrostatic shielding element is secured to the terminal cap with a gas-tight seal.

7. The combination of claim 5, wherein gasketing means is interposed between the end wall of the insulating casing element and the radially outwardly-extending flange portion of the electrostatic shielding element (112).

8. The combination of claim 5, wherein a weatherproof shield is secured to the radially outwardly extending flange portion of cup-shaped spring retainer (106) to prevent atmospheric contaminants from entering the spring area.

References Cited UNITED STATES PATENTS 2,257,652 9/1941 Rorden 17412 2,321,793 6/1943 Brandt.

3,009,983 11/1961 Oppel 174-12 X 3,160,701 12/1964 King et al. i 174-18 3,178,504 4/1965 Frakes et al. 17431 X LARAMIE E. ASKIN, Primary Examiner. 

1. A TERMINAL BUSHING INCLUDING AN AXIALLY-EXTENDING CONDUCTOR STUD, A HOLLOW SURROUNDING INSULATING CASING ELEMENT, A CUP-SHAPED TERMINAL CAP MEMBER SECURED TO THE END OF SAID CONDUCTOR STUD AND HAVING A CUP-SHAPED FLEXIBLE ELECTROSTATIC SHIELD SECURED THERETO WITH A GASTIGHT SEAL, SAID ELECTROSTATIC SHIELD HAVING A RADIALLY-OUTWARDLY EXTENDING FLANGE PORTION IN ABUTMENT WITH THE END OF SAID SURROUNDING CASING ELEMENT, SPRING MEANS ENCIRCLING SAID CONDUCTOR STUD AND DISPOSED INTERIORLY OF SAID CUP-SHAPED FLEXIBLE ELECTROSTATIC SHIELD FOR IMPOSING TENSILE STRESS UPON SAID CONDUCTOR STUD AND CORRESPONDING AXIAL COMPRESSIVE FORCE UPON SAID CASING ELEMENT IN- 